Their simulations of more than 20 million virtual “neighborhoods” demonstrate a troubling paradox: that community and diversity may be fundamentally incompatible goals. As the authors explain, integration “provides opportunities for intergroup contact that are necessary to promote respect for diversity, but may prevent the formation of dense interpersonal networks that are necessary to promote sense of community.”

Their models focus on the emergence of the “community-diversity dialectic” based on two simple principles: homophily – the tendency of people to bond with others like themselves – and proximity – the tendency of people to bond with those nearby. Their models look at how the strength of these basic tendencies affect the evolution of neighborhoods comprised of two distinct populations (say by race, class, ethnicity and so on). In these simulated neighborhoods, the possible levels of integration ranged from 0 percent (totally segregated) to 50 percent (totally integrated).

In the images below, the authors show three sample neighborhoods with low, medium, and high levels of integration. Notice how much denser the resulting social networks are (in the bottom row) in the highly segregated neighborhood at far left. (You can also play around with an interactive version of the model on Neal’s website, adjusting the levels of homophily, proximity, and integration yourself).

Figure 1: examples of simulated neighborhoods.

After 20 million-plus simulations, the authors found that the same basic answer kept coming back: The more diverse or integrated a neighborhood is, the less socially cohesive it becomes, while the more homogenous or segregated it is, the more socially cohesive. As they write, “The model suggests that when people form relationships with similar and nearby others, the contexts that offer opportunities to develop a respect for diversity are different from the contexts that foster a sense of community.”

The graph below, from the study, plots quite plainly the negative relationship between community cohesion and diversity.

in all reasonably likely worlds

These findings are sobering. Because homophily and proximity are so ingrained in the way humans interact, the models demonstrated that it was impossible to simultaneously foster diversity and cohesion “

But, of course, this is the result of computer simulations of reality, not reality itself. Our identities, social relationships and actual neighborhoods are far more complex than simulations can get at. And yes, diverse neighborhoods, while they may be scarce, do exist in the real world. Moreover, people don’t live in isolated neighborhoods of 500 homes, and segregation, diversity, and interpersonal relationships are phenomena that work on a far larger scale as well. But the fact of the matter is we sort ourselves into communities of similar, like-minded others. And this sorting process appears to be built into the very structure of our social lives.

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On a more positive note, it may be possible to have such sorting by neighborhoods and still have diverse cities. I asked Neal whether he thought that cities that were made up of a federation or mosaic of distinct neighborhoods were more likely to succeed than ones comprised of several more fully mixed neighborhoods. He told me that his model essentially predicted that, regardless of size, more segregated areas – be they neighborhoods or cities – will be more cohesive. He added in an email, “Or even, a more segregated earth will be more cohesive, and a less segregated earth will be less cohesive. Putting diversity and segregation together - you could have a metro that is cohesive and diverse, but it would also need to be highly segregated.”

Jane Jacobs liked to say that great cities are federations of neighborhoods.

If diversity is unattainable at the neighborhood level, might it be possible at the level of the city, as essentially a network of more or less similar neighborhoods? Jane Jacobs liked to say that great cities are federations of neighborhoods. It’s exactly what I see in vibrant cities like New York or Toronto. When I asked Neal about this, he sounded a more optimistic note: “Their patchwork of segregated communities allows for both diversity and cohesion. We usually view segregation as problematic, but when it comes in the form of a patchwork of neighborhoods and enclaves that each have their own character, it may actually ‘work.’”

For this reason, urbanists and local policy makers might be better off refocusing their efforts away from the unachievable ideal of diverse and cohesive neighborhoods and toward creating cohesion across the various neighborhoods that make up a city. In his watershed book Bowling Alone, Robert Putnam distinguished between two types of social capital: “bonding,” which occurs within like-minded groups, and “bridging,” which occurs between them. If, as the Neals’ study shows, we can’t make our neighborhoods more diverse and cohesive at the same time, perhaps the primary, over-arching, and achievable objective is to reinforce the bridging ties between them. Given the growing economic, cultural, and political divides within our cities and across the nation as a whole, working to strengthen the “bridges” between communities may be a far more realistic approach than attempting the impossible task of trying to make everywhere more diverse.

About the Author

Richard Florida is a co-founder and editor at large of CityLab and a senior editor at The Atlantic. He is a university professor in the University of Toronto’s School of Cities and Rotman School of Management, and a distinguished fellow at New York University’s Schack Institute of Real Estate and visiting fellow at Florida International University.

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